The article investigates a number of documents contained in the Archive of Foreign Policy of the Russian Empire — thus, introducing the materials into scientific discourse — and explores the nature of Russo-Korean relations and the activities of Russian diplomacy in Korea on the eve of and during the Russo-Japanese war of 1904–1905. The article argues that Russia’s main goal regarding Korea was to preserve its independence and territorial integrity. The paper primarily seeks to to show the efforts of Russian diplomacy during the period undertaken to ensure the independent existence of the Korean state and prevent the final transition of the country under the rule of Japan. As the author points out, Russia was the first among the powers to recognize the neutral status of the Korean state, being the only power to have condemned Japan’s violent course of action in immediate aftermath of its initiated hostilities and proclaimed it be illegal to seize power in the independent Korean state that had declared itself neutral. The article consistently examines the active support by Russian diplomats to the attempts of the Korean emperor Gojong to preserve the independence of the country, their opposition to the persistent attempts of the Japanese authorities to intimidate Gojong to conclude an agreement on the establishment of a Japanese protectorate over Korea. The work provides convincing evidence of the important contribution by Russian diplomats to the establishment of deeply trusting relations between the Russian and Korean imperial houses. Their honesty, decency, sincere concern for the welfare of Korea and its security proved efficient to win the favor and friendship of the Korean emperor who had repeatedly asked for asylum in the Russian mission in case of personal danger and even about assistance for resettling him towards Russia. The paper demonstrates the understanding by Russian diplomacy of the national-state interests in the region which resolved into preventing Korea from becoming a springboard for hostile actions against Russian Far Eastern possessions, analyzes the role of Russian representatives in developing Russia’s position on recognizing the neutral status of the Korean state as a measure to counteract the calculations of the Japanese Government to tie Korea by allied commitments in the event of hostilities and establish its protectorate over the latter. The article highlights in detail the joint efforts of Russian diplomats undertaken along with the French mission in Seoul in the absence of the Russian mission there aimed to defend the interests of the Russian Government and private Russian-nationals in Korea. In addition, the article mentions the efforts of Russian diplomats and agents to provide the Russian Government with accurate data about the plans and capabilities of the Japanese top military to prepare a base in Korea for a future war, in particular, on the disclosure of areas where enemy units were located, and on developing routes, providing troops with food supply in Korea in future defensive campaigns. Particular attention is paid to showing the aggressive policy of Japan in Korea.